This brief journal communication describes the eukaryotic diversity of Spain's Rio Tinto, which is surprisingly greater than that of the prokaryotes. Morphology and molecular- based investigations are introduced and results are shown in the form of a minimum-evolution analysis phylogeny. The article challenges former ideas about the phylogenetic range of organisms that are capable of living in extreme environments. A subscription to nature - http://www.nature.com - is needed to view this resource.